1. Field of the Invention
The present invention relates to a solid-state imaging device. More particularly, the present invention relates to an imaging apparatus or the like to be used for a digital still camera or a digital video camera.
2. Description of the Related Art
Distance detection techniques for AF (automatic focus settings) are known in the field of digital still cameras and video cameras. With regard to distance detection techniques for AF, Japanese Patent Application Laid-Open No. 2009-158800 proposes a ranging device realized by making part of the pixels of an imaging device have a ranging function that allows the device to be capable of detecting the distance to a subject by way of a phase difference detection type process. With a phase difference detection type process, images of the light fluxes that pass through different areas on the pupil of the imaging optical system of an imaging device are compared to detect the distance to a subject by means of triangulation using 3D images. With such a device, the distance to the subject is effectively measured unlike conventional contrast detection type devices because the lens of the camera does not need to be moved for focusing. In other words, high speed and high accuracy AF setting operations as well as real-time auto-focusing during video shooting can be realized with such a device. The above-cited Japanese Patent Application Laid-Open No. 2009-158800 discloses a ranging pixel including a micro lens, a waveguide and a plurality of photoelectric conversion sections such that the waveguide and the plurality of conversion sections are arranged below the micro lens. By using such ranging pixels, light fluxes that pass through different areas on the pupil of the imaging optical system are respectively guided to corresponding photoelectric conversion sections to make it possible to measure the distance to a subject.
However, the arrangement described in Japanese Patent Application Laid-Open No. 2009-158800 is accompanied by a problem that the ranging accuracy is degraded in peripheral sections of the imaging device and also in instances where a large number of light fluxes enter ranging pixels with large incident angles such as when a very light imaging optical system is employed. Such light fluxes can easily be bound to higher order eigenmodes of a waveguide and propagated through the waveguide in a guided mode with a broadened electric field distribution to get to a plurality of photoelectric conversion sections in a pixel. Then, the light fluxes that pass through different pupil areas can hardly be selectively guided to different photoelectric conversion sections to consequently degrade the pupil division characteristic. As a result, the base line length of triangulation is apt to become short to consequently degrade the ranging accuracy.
In view of the above-identified problem, the object of the present invention is to provide an imaging device that can accurately conduct ranging operations in ranging conditions that involve a large number of light fluxes entering ranging pixels with large incident angles particularly if the pixel size is small and a ranging device or the like that is realized by using such an imaging device.